The invention relates to a lubrication system for a differential of a driven axle. The invention also relates to an automotive vehicle equipped with such a lubrication system.
Automotive vehicle such as cars or trucks are generally equipped with one or several differentials on their driven axles. Differentials need lubrication in order to prevent damages such as scoring on the various elements of the differential. Differentials are commonly lubricated by splash lubrication. The differential is for example contained in an axle housing having a central part in the shape of a bulb which forms a sump partly filled with lubricant. The crown wheel, which forms the outer part of the differential, has its lower part immersed in the lubricant of the sump so that, when it rotates, it splashes the lubricant all over in the central part axle housing, thereby lubricating various parts of the differential. In case of transmission of high torques in the differential, a high level of lubrication is needed. In this case, lubricant must be provided in a large amount on various areas of the differential, in particular at the interface between gears, such as at the interface between a pinion driven by the motor of the vehicle and a crown wheel, or the various bearings which support the rotating parts of the differential. This is achieved by making sure that the right amount of lubricant is contained in the sump and splashed by the crown wheel. In case a low lubrication level is needed, for example, when low torques are to be transmitted, too high an amount of lubricant induces excessive power losses due to the resistance of the lubricant to the rotation of the crown wheel, which partially takes place in the lubricant.
To limit the power losses when low lubrication level is needed, lubrication systems known for instance from WO-A-2010/106482 use a lubricant tank arranged inside the sump containing the differential. This tank is permanently filled with lubricant by the rotation of the crown wheel, which spins the lubricant into the tank thanks to its teeth. The tank can retain a part of the lubricant which is thereby removed from the sump and removed from contact with the crown wheel. Thereby the amount of lubricant effectively involved in the lubrication is reduced, and the power losses due the crown wheel splashing the lubricant are reduced. In case of heavy duty, a high lubricant flow rate can be provided by partially emptying the tank to raise the lubricant level in the sump. The tank includes to this end electronically-controlled valves for passing the lubricant from the tank to the sump. Such a lubrication system does not provide a satisfying lubrication at the interface between the crown wheel and the pinion, in the bearings of the pinion and in the interior of the differential, because these areas are not easy to access. The lubricant does not always reach these areas. Therefore, this can lead to scoring on the elements of the differential, and to critical heating of the pinion bearings, which are located in a place which is generally above the lubricant level in the sump. Moreover, the electronic control of the transfer of lubricant from the tank to the sump is complex, expensive and not always perfectly reliable.
It is desirable to provide a new lubrication system for a differential of a driven axle on an automotive vehicle, allowing to properly lubricate critical areas of the differential and to adapt the lubrication level to the various operating configurations of the differential.
An aspect of the invention concerns a lubrication system for a differential of a driven axle on an automotive vehicle, comprising a sump in which is located a crown wheel driven by a pinion, the crown wheel being fast in rotation with a carrier, and a main lubricant tank located in the sump, having an inlet port and at least one outlet port, rotation of the crown wheel causing lubricant to be transferred from the sump to the main tank via the inlet port, and the outlet port allowing the lubricant to pass from the main tank to the sump. This lubrication system is characterized in that it comprises:
an auxiliary lubricant tank located in the sump, adapted to be filled in with lubricant by rotation of the crown wheel, and
means to convey lubricant by gravity from the auxiliary tank to a lubricant needing portion of the differential.
Thanks to an aspect of the invention, the auxiliary lubricant tank is filled by the rotation of the crown wheel and allows an efficient lubrication, by gravity, of critical parts of the differential, such as the pinion bearings and/or the interior of the differential, by directly bringing the lubricant to these areas. This permits to improve the lubricant level management.
According to further aspects of the invention which are advantageous but not compulsory, such a lubrication system may incorporate one or several of the following features:
The auxiliary tank is located in the main tank, whereas lubricant is transferred to the auxiliary tank by the rotation of the crown wheel via the inlet port of the main tank.
The auxiliary tank is located in an upper area of the main tank.
The lubricant needing portion comprises one or several of an interior volume of the carrier and/or of a bearing.
The means to convey lubricant, to the interior volume of the carrier, comprise at least one pipe adapted to convey the lubricant from the auxiliary tank to an area above at least one of two wheel axles of the differential outside the carrier, whereas said wheel axle comprises a thread, realized on an outer peripheral surface of said wheel axle, and adapted to convey lubricant towards the interior of the carrier during the rotation of said wheel axle.
The means to convey lubricant, to a bearing allowing the rotation of the pinion, comprise at least one pipe adapted to convey lubricant from the auxiliary tank to an area in the vicinity of a shaft driving the pinion.
The auxiliary tank is adapted to empty itself in the main tank when it is overfilled.
The carrier comprises, on an inner surface, lubricant stopping elements adapted to prevent lubricant from getting out of the interior of the carrier.
The carrier comprises, on a surface facing the or each wheel axle, holes for allowing lubricant to get in the interior of the carrier.
The main tank is equipped with means for transferring lubricant to the sump when a rise of the lubricant level in the sump is needed.
The means for transferring lubricant from the main tank to the sump comprise at least one thermostat.
The lubrication system comprises two thermostats mounted on the main tank and adapted to open or close on the basis of the temperature of the lubricant in the sump.
The two thermostats are adapted to maintain the main tank open when the lubricant temperature in the sump is below a first temperature or above a second temperature superior to the first temperature.
The main tank is C-shaped.
An aspect of the invention also concerns an automotive vehicle comprising one or several differentials. The vehicle is characterized in that it comprises one or several above-mentioned lubrication system.